Morris Minor Owners Club

Hi all i had to get the AA out the other day as my car just died , absolutely nothing . The nice AA man tested the dynamo as the red warning light was on when he jump started the car , he said the dynamo wasn't charging , i managed to get the car home , bought a new battery to be on the safe side , changed the brushes in the dynamo , cleaned the commuter with petrol on cloth , cleaned all the connectors, put back together and still the red light is on! I don't have a tester to check the volts etc also i don't know how the car is negative earth , ive also tried tapping the contact in the control box but the light doesn't go out. Can some kind person tell me what to try next ? The fan belt is tight without being over tight , many many thanks in advance Joanne

Possibly the controlbox is knackered. If you take the cover off the contacts should close when you rev the engine and open on tickover.
Check for disconnected wires.
Check the back of the control box for damage to the circuits

Thanks Mike i'll have a look at that tomorrow but im starting to think that an alternator conversion is in the pipeline lol

If you do a lot of winter driving in the dark with the lights, heater, wipers etc on then an alternator is worth considering. Otherwise a dynamo should be OK.

i think alternators are better altogether

I drive the car everyday (when it works lol ) and i have a radio and cig lighter for the sat nav fitted , im just thinking that by the time i have bought a new control box and maybe a dynamo i may as well just pay for the alternator kit. I am assuming this is relatively easy to fit?

None of these justify an alternator - but if you can find a cheap one - get it in stock! I pay £1 for mine - search autojumbles. Check for dynamo output with a voltmeter on the battery terminals. Expect 13.8/14 volts with the engine doing more than idling revs.

You cannot guess if the dynamo is charging - You need a meter or take it to a garage (or even Halfords) and get them to check if the battery is been charged.... Once we know one way or the other we can advise on what to do next.....

joannebinney wrote: I don't have a tester to check the volts etc

I think a meter is pretty much essential, they're not expensive and once you have one you'll find you use it all the time

I will get a meter today , the AA man did test the dynamo and said it wasn't charging , i'll post the readings later today , i'd like to find an alternator for £1! Bmc

I suspect that the £1 alternators can be found in Loch Ness

i had exactly the same symptoms, well my car did.

we check the bat, changed brushes on dynamo, motored it, checked output, the whole shabang.

new control box on order from bull motif, 25 quid or there abouts.

good luck.

Thanks for that Archie76 if all else fails i'll try a new control box , i'm glad to know its not just me that has tried (and failed lol ) with everything else

If a dynamo 'motors' then it's working! Besides 'control box' the only other possibility is a broken wire connection.

Dynamo's tend to work muc more reliably than alternators, so my preference is to keep them
Mains charging the battery (on the car) once or twice over winter takes a lot less time than fitting an alternator - and a lot less time than waiting for the AA to rescue you when the alternator packs up (which they do - far more often)

However I know I'm in the minority for preferring dynamo reliability to Alternator output ;-)

oh its not so bad waiting for the nice AA man to come , i work for the AA so i tend not to have to wait too long lol

I had exactly the same problem with my car. I took the cover off the control box. There are two coils under there and (if memory serves correctly) the right hand coil as you look at it is the one the cuts out the dynamo at low revs. It needs that otherwise the dynamo actually flattens rather than charges the battery. I cleaned up the points at the top of the coil with a bit of sandpaper. That actually didnt do the trick but I then took a screwdriver and closed the points with the engine revving fairly quickly. Once I had done that for it, it seemed to work on it's own from there on and is charging fine now. It saved me buying a new control box.

culp wrote: I cleaned up the points at the top of the coil with a bit of sandpaper. That actually didnt do the trick but I then took a screwdriver and closed the points with the engine revving fairly quickly. Once I had done that for it, it seemed to work on it's own from there on and is charging fine now. It saved me buying a new control box.

The point on a regulator should only be cleaned with a piece of stiff card.

Hi,
try taking the dynamo to bits again and have a look at the commutator (the thin copper strips at the end of the field windings where the brushes rub) even if you've cleaned then and fitted new brushes then they may be ineffective.

It's a common problem caused by them wearing as they rotate against the brushes.
There are strips of mica (like bakelite) between the copper sections which act as insulators, the mica should be slightly lower than the copper surface, I bet it isn't?

Treating this is a doddle, you get a VERY thin file or a snapped off hacksaw blade (wear eye protection if you're going to snap it yourself) and use the back of the blade - NOT THE TEETH - to scrape the mica back until it's abour 1-2 mm maximun beneath the surface of the copper sections, the book says the bottom of the slot should be flat, hence the use of the blade's back!

On another note, you'll probably have a groove around the copper plates where the brushes have worn, you can get this machined back on a lathe or hold the whole thing in a vice and use glass paper (not wet & dry or carbide) as this will not leave any dust to earth the copper,segments.
Cutting back the mica happens after you've fettled the copper sectors, of course.

Hope this helps, I like dynamo's as they are so easy to work on and normally adequate for the job. As long as it's not pouring with rain, I can normally carry out the above 'out, strip, overhaul, sand, undercut mica, re-brush, assemble and re-fit in 30 minutes.